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On the thermal structure of Triton's thermosphere
Author(s) -
Stevens Michael H.,
Strobel Darrell F.,
Summers Michael E.,
Yelle Roger V.
Publication year - 1992
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/92gl00651
Subject(s) - thermosphere , atmospheric sciences , atmosphere (unit) , tropopause , physics , mixing ratio , thermal , ionosphere , astrophysics , thermodynamics , astronomy , stratosphere
The analysis of the Voyager 2 Ultraviolet Spectrometer (UVS) solar occultation data obtained at Triton is consistent with a spherically symmetric, isothermal thermosphere above 400 km at T ∞ . = 96 K. A detailed calculation of energy loss processes in a pure N 2 atmosphere, heating and cooling rates, and resultant thermal structure associated with solar UV irradiance and magnetospheric electron precipitation indicates that solar heating, with calculated T ∞ = 70 K, is insufficient to account for the inferred T ∞ = 96 K. The magnetosphere must deposit twice as much power as the sun (λ < 800 Å) to heat the thermosphere to 96 K and generate the observed N 2 tangential column densities above 450 km. The thermal escape of H and N atoms and the downward diffusion of N atoms to recombine below 130 km results in local ionospheric heating efficiency of 24%. An upper limit on the tropopause CO mixing ratio of 2 × 10 −4 is inferred in the absence of aerosol heating to balance its efficient cooling by LTE rotational line emission.